1. Field of the Invention
This invention relates to close-up photography devices for use in either close-up photography or macro photography of an object.
2. Description of the Related Art
In photography exceeding 0.2.times.magnification but below about 10.times., or so-called close-up photography, intermediate device has been used to widen the distance between the film plane in the camera and the photographic lens (lens barrel). As this intermediate device, generally the bellows-type extension device expansively connecting the mount coupler on the camera with the mount coupler on the lens barrel through a bellows of light shielding material, or the so-called intermediate tube intervening between the camera body and the photographic lens is widely used. Since the photographic magnification is determined by the amount of extension of the photographic lens, with the former or in the case of the bellows type, by adjusting the extension of the bellows, while with the latter, or in the case of the tube, by altering the tube length, the photographic magnification is set to a desired value before shooting.
FIG. 4(a), FIG. 4(b) and FIG. 4(c) are diagrams of a model to explain the correlation of the amount of extension d of the photographic lens and the photographic magnification .beta..
The photographic lens L of focal length f forms an image Y of an object Y.sub.0 on a film plane F as the image plane. "a" denotes the object distance (the distance between the photographic lens L and the object Y.sub.0). "b" the image distance (the distance between the photographic lens L and the film plane F), and "l" the shooting distance (the distance between the object Y.sub.0 and the film plane F).
FIG. 4(a) shows a position of the photographic lens L where the amount of extension d=0, or the focus of the lens L lies on the film plane F so that the photographic magnification .beta.=1/.infin.. FIG. 4(b) and FIG. 4(c) show different focusing movements of the lens L, FIG. 4(b) being depicted for about 1.times. photographic magnification, and FIG. 4(c) for 2.times. one.
The, the photographic magnification .beta., the shooting distance "l" and the object distance "a" are correlated to each other by the following equations: EQU .beta.=Y/Y.sub.0 =b/a=d/f . . . (1) EQU l=f(1+.beta.).sup.2 /.beta.. . . (2)
Rearranging the equation (2) with the shooting distance l as a constant, the functions for f and .beta. are obtained, graphically shown in FIG. 1. If, as the amount of extension d of the lens (the amount of increased distance between the photographic lens and the film plane (image plane) measured from the position for the photographic magnification of 1/.infin.), increases, the focal length f of the photographic lens L is made to alter in such a way that it first increases and then decreases, the photographic magnification can monotonously be increased without having to vary the shooting distance l.
Since the optical equation (2) is the image forming equation, the image plane of sharp focus is not caused to shift by varying the forward movement d.
FIG. 2 is a diagram of an optical system model exemplifying a varifocal photographic lens as the photographic lens L, comprising lens groups L.sub.1, L.sub.2, L.sub.3 and L.sub.4 each consisting of one lens element or a plurality of lens elements. D stands for a diaphragm. By moving all of the first lens group L.sub.1, the second lens group L.sub.2, the third lens group L.sub.3, the fourth lens group L.sub.4 and the diaphragm D, the focal length f is varied, or variation of magnification is effected.
The operating positions (a), (b) and (c) shown in FIG. 2 have values f.sub.1, f.sub.2 and f.sub.3 of the focal length f of the lens L respectively, which lie on the graph of FIG. 1. The optical arrangements of (a) and (c) are conjugate to each other where the relationships of f.sub.1 =f.sub.3 and 1/.beta..sub.1 =.beta..sub.3 are established. Also, .beta..sub.2 =1.times.. When varying the magnification, the second lens group L.sub.2, the third lens group L.sub.3 and the diaphragm D linearly move in unison, while the first lens group L.sub.1 and the fourth lens group L.sub.4 move entirely symmetrically to each other with respect to the second lens group L.sub.2, the third lens group L.sub.3 and the diaphragm D so that at the position (b) of unity magnification, the variable lens spacings both become shortest. Further, the first lens group L.sub.1 and the fourth lens group L.sub.4 are so arranged that their movement on the optical axis o-o relative to the second lens group L.sub.2, the third lens group L.sub.3 and the diaphragm D from the photographic magnification .beta..sub.1 to the .beta..sub.2 (life-size) is equalized to that from the .beta..sub.3 to the .beta..sub.2 (life-size). In other words, the positions for each of the aforesaid values of the photographic magnification of the first lens group L.sub.1 and the fourth lens group L.sub.4 relative to the second lens group L.sub.2, the third lens group L.sub.3 and the diaphragm D vary as shown in FIG. 3. Also, at that discrete values of the photographic magnification and any other values therebetween, the distance between the object and the predetermined image plane is always constant, so that once the sharp focus has been established, later alteration of the magnification does not require re-adjustment of the focus.
In close-up photography, to make the optical system move in the above-described way as shown in FIG. 2 and FIG. 3, while the movement of the second lens group L.sub.2, the third lens group L.sub.3 and the diaphragm D is done by the bellows (intermediate device), the movement of the first lens group L.sub.1 and the fourth lens group L.sub.4 should be done by operating a cam mechanism mounted on the movable side of the bellows. Thus, the movement of the first lens group L.sub.1 and the fourth lens group L.sub.4 shown in FIG. 2 is realized by the combined motion of the bellows and the cam mechanism.
The general form of the cam mechanism for this purpose is shown in an expanded view of FIG. 14. A fixed portion 201 has a straight slot 201a of direction along the optical axis o-o. A cam tube 202 is only rotatably supported relative to the fixed portion 201. A cam slot 202a is formed in the cam tube 202. A reference numeral 203 is a pin of a movable lens group tube. The motion of this pin 203 is the same as that of the magnification varying lens group (L.sub.1 or L.sub.4) held in the movable lens group tube. The aforesaid pin 203 penetrates the straight slot 201a of the fixed portion 201 and fits in the cam slot 202a of the aforesaid cam tube 202. In this state, when the cam tube 202 rotates in a direction of arrow B, the pin 203 is moved first in a direction of arrow C and then in the opposite direction of arrow E. Therefore, the magnification varying lens group, too, is moved in a similar way to that of the pin 203.
As has been described, such a movement of the first lens group L.sub.1 and the fourth lens group L.sub.4 is realized.
By the way, with the conventional simple extension device of the bellows type or the tube type, when the photographic magnification .beta. is altered, the shooting distance l is caused to change. Therefore, the camera position has to be changed along with it.
That is, when the photographic magnification .beta. is altered by varying the amount of extension d of the lens, the shooting distance l changes by the equation (2) mentioned before. This means that the distance l from the object Y.sub.0 to the film plane F, or the position of the camera, must be altered. In close-up photography, because the photographic magnification .beta. is high, when shooting, camera shake is apt to occur. Also, for another reason that keeping hold of an image of a very small object within the picture frame becomes difficult, generally, a tripod or other stabilizing device is used for the purpose of maintaining the camera or the close-up photography device stationary during shooting. Hence, the operation of adjusting the position of the camera to the sharp focus again in accordance with change of the shooting distance l resulting from the alteration of the photographic magnification tends to carry the stabilizing device such as a tripod itself away from the current position. To do this, the stabilizing device such as a tripod and its load, namely, the camera, the photographic lens and the intermediate device for close-up photography, totaling a very heavy weight, are troublesome to displace. Also, as this displacement often makes the very small object out of alignment with the picture frame, determination of the composition must be made again, and focusing must be carried out. It is inconvenient to resume all the preparation prior to making an exposure. Further, by vibrations produced when moving the stabilizing device such as a tripod, the very small object moves away, thus disturbing a set state for shooting. Unfavorable situations like this may be encountered with a high possibility.
In short, it has been the conventional practice that in the case of using the intermediate device in combination with a varifocal photographic lens attached thereto, each time the intermediate device is operated, a very inconvenient process must be carried out which comprises the steps of detecting the amount of extension d the lens has moved forward by reading the scale on the intermediate device and then controlling the varifocal photographic lens in accordance with the detected amount of extension d to adjust its focal length to a predetermined value. Also, during doing this, a manipulation mistake is apt to occur. Incidentally, the idea that the optical system is moved so as merely not to change the focus state when varying the magnification is known in Japanese Laid-Open Patent Application No. Sho 63-189848.
Also, in the structure of the cam mechanism exemplified in FIG. 14, a large angle .THETA. the tangent direction of the cam makes with the straight slot 201a is required to make the movement of the pin 203 smooth. This tends to increase the length L in the circumferential direction of the cam slot 202a. In general, a plurality of cam mechanisms of these members must be arranged. To increase the length L is to produce a problem in space. Also, as the length L in the circumferential direction of the cam tube decreases, the angle the tangent direction of the cam slot makes with the straight slot 201a decreases, causing the pin to become difficult to move and further causing the position accuracy of the pin to become worse which in turn lowers the position accuracy of the movable lens group, too, thus giving a problem in that the optical performance deteriorates.
Also, the bellows have generally a distance scale on the rail thereof for assistance in adjusting the photographic magnification. With the help of this distance scale, the photographer reads the amount of extension d of the bellows. And, from the read value of the amount of extension d and the focal length of the lens, he calculates the photographic magnification .beta.. It is also general that along with the distance scale, there are displayed values of the magnification when the exclusive lens is in use. In this case, there is no need to read the amount of extension d and calculate the resultant value of the photographic magnification .beta. (as, for example, disclosed in Japanese Patent Publication No. Sho 58-7372.).
However, since, in the above-described conventional example, the distance scale or the magnification display is on the top surface or side surface of the rail, the bellows becomes a hindrance in confirming the current value on the distance scale or by the magnification display from the position the photographer's eye usually takes. So he is obliged to look either right from the side, or diagonally from the upper side. Hence the visual confirmability is very poor.
Also, as one of the important factors for realizing the close-up photography device based on the above-described principle of variation of the magnification while still preserving high reliability and accuracy, mention may be made of assurance of the desired accuracy with which the interlocking members of the intermediate device and the lens barrel (variable magnification lens, varifocal photographic lens), when coupled with each other, are initially set, and removal of the "play" such as mechanical backlash.